1. Field of the Invention
The invention particularly concerns the use of a water-based adhesive for adhesively edge-padding a stack of collated paper, especially carbonless paper, so that upon being fanned out, the stack spontaneously separates into individual sets, each set being adhesively bonded together at one edge.
2. Description of the Related Art
U.S. Pat No. 4,217,162 (Glanz et al.) says: "For many years carbonless copy paper has been made into form sets from a lift of collated sheets by applying an adhesive to one edge of the lift, drying the padded edge and fanning the lift into individual form sets. British Pat. No. 1,263,510 discloses an improvement in edge-padding performance by using as the adhesive a mixture of an aqueous solution of a gelatin derivative and an aqueous emulsion of a polymer. Further improvements in edge-padding are taught in U.S. Pat. Nos. 3,960,638; 3,963,553; 3,970,500; 3,970,501; and 4,041,193 where a naphthalene sulfonic acid-formaldehyde condensate is used in an edge-padding adhesive formulation in various combinations with materials such as water-soluble polymers, water-soluble binders, water-soluble metal salts, polymer emulsions, surface active agents and latexes. Japanese Pat. Publication Nos. 12844/1978 [JP 78012844] and 12845/1978 [JP 78012845] teach the use of a surface active agent with an aqueous solution of a synthetic polymeric adhesive, respectively, in an edge-padding adhesive formulation. Japanese Pat. Disclosure No. 99635/1974 [JP 49099635] teaches an aqueous edge-padding adhesive composition comprising a vinyl acetate/maleic acid copolymer and various alcohols" (col. 1, lines 19-43).
Like the adhesive compositions mentioned in the foregoing quotation, that of the Glanz patent is a water-based adhesive but is said to provide better bonding within a set and better separation between sets when the edge of the lift or stack is pretreated with water or certain aqueous solutions before applying the adhesive. The Glanz patent says: "Selective adherence occurs because the adhesive bonds the coated surfaces of the collated form, but not the uncoated surfaces" (col. 2, lines 29-31). Except for that statement, neither the Glanz patent nor any of the above-cited patents or publications explains why the adhesive adheres only to the coated surfaces.
Chem Abstracts, Vol. 99, Abstract 185057J (1983) reports that Japanese Pat. Application 81/160,004 [JP 81160004] (Fuchigami; also PCT Int. Application WO 83 01,228) uses an aqueous latex adhesive to bond the edge of a stack of carbonless or no-carbon-required (ncr) paper that can be fanned apart into individual sets. The abstract says that "the outside surfaces of the copying paper set are coated with water resistant and/or water repellent substances to prevent adhesion between sets."
In collated carbonless copy papers currently on the market, at least one of the outer faces of each set typically has been treated with a silicone, fluorocarbon or some other coating which counteracts curling that otherwise would result from the functional coating on the other surface of that sheet. That treatment also acts as a release agent for the edge-padding adhesive and can allow the adhesively edge-padded stack to separate into sets upon fanning, assuming that the edge-padding adhesive is not so thick as to create bridges that would inhibit such separation. Failures to separate are quite common.
Several adhesive compositions are currently marketed specifically for the purpose of edge-padding collated stacks of carbonless copy paper to be fanned into sets. Of these, the following are predominant in the U.S. market: "Mead Fan-Apart Adhesive" from the Fine Paper Division of Mead Paper Corp., Chillicothe, OH; "Fanapart High-strength Padding Adhesive" from Appleton Papers, Inc., Appleton, WI; and "Fan-Out Padding Adhesive" from 3M. Each of these is a water-based adhesive composition. Unfortunately, each of these adhesive compositions is specifically formulated for use with carbonless copy paper marketed by the same company, and is not satisfactory for use with carbonless copy paper of another company. When so used, the adhesively edge-padded stack may either fail to fan apart or individual sheets within the sets may separate prematurely, e.g. when subjected to crash-imprinting.
It is believed that the carbonless copy paper marketed by each of these three companies has a fluorocarbon coating on at least one of the outer faces of each set, which coating acts as a release agent when an edge-padding adhesive is applied.
The aforementioned dominant edge-padding adhesive compositions have been analyzed and are believed to have the following approximate compositions:
______________________________________ % by wt. ______________________________________ "Mead Fan-Apart Adhesive" poly(ethylacrylate/methylacrylate) (92/8) 13 1,2-propanediol 19 ethyl alcohol 7 water 61 "Fanapart . . . " from Appleton poly(ethylacrylate/N-methylolacrylamide) 17 1,2-propanediol 28 ethyl alcohol 8 water 47 "Fan-Out Padding Adhesive" from 3M poly(ethylene/vinyl acetate) stabilized 9 with surfactant poly(vinyl alcohol) 4.5 ethyl alcohol 28 crystalline sorbitol, 4000 NF 1.25 water 57.25 ______________________________________
In each of these adhesive compositions, the first-named ingredient is a water-based latex adhesive polymer. The monohydric alcohol increases the rate of penetration and enhances drying. Each of the polyhydric alcohols, including sorbitol, has a Hansen dispersion solubility parameter close to that of the polymer and thus may serve to plasticize the edge-padding adhesive. The poly(vinyl alcohol) of the 3M adhesive is a low molecular weight, water soluble, polymeric, polyhydric alcohol and may also act as a viscosity control agent.